Multi-pole fine magnetic scale for high-resolution magnetic encoders evidenced by a simplified method

Abstract

Magnetic encoders are widely used in linear and rotary positioning applications, specifically under harsh environments. The finer the magnetic pole-pitches of the magnetic scale in magnetic encoders the higher the resolution of the encoder. Conventional non-structured magnetic scales can be achieved with ease by dedicate magnetizing fixture at a pole pitch larger than 1 mm. It becomes extremely difficult to magnetize the poles with pitch much <1 mm, say, 0.1 mm. We propose a simple magnetic grating structure to alleviate this difficulty and verify its feasibility. The magnetic grating was first designed according to the demagnetization curve of a permanent magnet with proper dimensions to attain high magnetic flux density. Simulation results showed that periodical signal of sinusoidal nature can be obtained from such a magnetic grating being magnetized by merely a single magnetizing the grating as a whole. The periodicity conforms to the 1:1 ratio of pole-width and groove-width. Magnetic flux density in z direction increases enormously with decreasing detection gap. These results are significant for signal processing. Experimental results by using a simplified verification method confirm the simulated results. Instead of by magnetizing, the precision of such a magnetic encoder is governed solely by the precision of machining the pole-groove structure. The proposed method can thus be easily achieved by various high precision machining methods such as wire-EDM, laser-beam machining, or photo-lithography, and etc.